Substation circuit



March 14, 1944.

A. E. WOODRUFF SUBSTATION CIRCUIT Filed Aug. 5-, 1942 INVENTOR. ALBE T E. WOODRUFF i 4% Z ATTORN Y '463 .turns from the other end turns to, a circuit including receiver winding. It has alsobeen round that it.

level is nearly I quency range to theresponse'characteristics at the higher level, thereby, maintaining substan- 68 Patented Mar 1 I: v V

UNITED STATES. PATENT v OFFICE.

suns'ra'rron cmcurr Albert E. Woodmfl, Oak Park, 111., asslgnor to An tomatlc Electric Laboratories, Inc., a corporation of Delaware Application August 5, 1942, Serial No. 453.818 'Y a Claims. ('01. ire-'81) The present invention relates to substation telephone circuits in general but more partlcularly to portable field telephones and in which the portable substation circuit may be connected to line: varying greatly in length.

Efllcient'sound translating devices have been used in'a battery-less telephone system wherein no batteries are needed for transmission or receipt of telephone messages. A magnetic or sound powered receiver used in this type of system is tially the same characteristics or the receiver shown in the Woodrufi et al. Patent 2,241,105.

It has been found that when a. sound powered receiver, suchas disclosed in. Patent 2,241,105, is substituted for a regular telephone receiver in a. telephone system using battery for talking purposes, the output level oi the sound powered re ceiver is from 12 to 15 decibels higher than the regular receiver. Due to this high output level, this type of receiver than the regular receiver.

, On short. lines the output level of the receiver is can be'used on longer lines too high and is an-' noying. unless of course the user is partially deaf.-

I. circuit comprises the hand generator G, ringer in, auto-transformer windings it, it and it, the

For ordinary-useon short lines it is necessary to I reducethe output level 01' the sound powered receiver and themethod used'in the present invention is the nus-matching oi impedance. A tap isput on the receiver coil windingat a-point to produce approximately a 12 decibel loss due to mis-matching of impedance. For example, the receiver coil winding may turns when its impedance-.-is properly matched to its circuit and the tap. for introducing the 12 decibel loss, would be connected to the coil winding between '77 turns from one end terminal and terminal or the receiver winding. Therefore in the above example, on short lines only about one-seventh, or 77 turns, of the receiver winding is used in the receiver circuit to. reduce the output level of the receiver. On long lines all the turns of the receiverwindings are included in the receiver circuit thereby using the full and proper matching impedance to give the maximum efiiciency and output. 'A switching key is. provided-on the handle or the handset between the transmitter and receiver for switching iron the 'normallow impedance .tap connection comprisingyonly aportion oi-the receiver coil all thetums of the the loss is introduced by impedance nus-matching the loss is include a total 0:540

nearly independent of frequency.

and that the response characteristics at the low parallel throughout theuseiu m1.

former is inductively circuit lirom one terminal torboth high and low levels.

means for mis-matching the sound powered receiver with with a manui'or including the impedance which ally operable switching means full receiver winding having an is properly matched to its circuit to increase the output 'level oi the sound powered receiver when v used on long lines. This and other is diagrammatically-represented a portabletelephone substation circuit of the local battery type. Referring now to the drawing, the substation and the handset including'the transnected to form a local battery substation circuit of the anti-side tone type. The autoqtransformer comprises three inductively coupledwindings it serially included with, condensers 9 and it in a circuit connected betweenthe line conductors i and 2. The transmitter T and battery B' in series with the transniitterkey 6 is connected in shunt of the primary winding NY or the auto-transformer and the receiver including .the volume control receiver switch- 3 is shunted by the secondary winding i2 01 the auto-transformer and condenser 9. The ringer I0 is bridged across the line conductors I and 2 for giving an audible indication on incoming calls. The hand generator G and generator switch 20 are for use in transmitting signalling current over theline conductors on outgoing calls.

The secondary winding it of the auto-transcoupled to the primary winding l4 and the secondary winding i2 is also inductively coupled to the primary winding 14. The winding i2;ha's a numbe'r of turns 01' line wire forming a relatively high resistance wlnd-- reierredto astheartincialline. i Considering'the action oi'the substation-during transmission. the transmitter thumb switch 8 is a local direct current,

oi battery thru'atheing whichtogetherwith thecondenser 9' forms a balancingcircuit, such circuitbeing. commonly closed thereby completing lines by norobiectswill bemorereadily'understood by reference to the. following detaileddescription and the associated drawing inwhich receiver R, transmitter switch 8 and transmitter T, the switch 6, primary winding I4 to the other terminal of battery. The action of the voice on the transmitter causes it to vary this direct current changing it into undulating current, which upon flowing thru the winding I4, induces in the windings I2 and I3 an alternat ing current of proportional strength. The autotransformer action of the windings I2 and I3 amplifies the variations in current strength produced in the winding I4. This current flows over two circuits, one over line conductor I thru the external line circuit to line conductor 2, condenser I5, to the portion I of the receiver coil winding of receiver R, coils I4 and I3; and the other over winding I2 of the auto-transformer, condenser 9, to the portion 1 of the receiver coil winding back to winding I2. It will be noticed that the receiver is included in both these circuits and that the current flow in these two circuits are in opposition. If the artificial line, previously mentioned as being built in the winding I2, is equivalent to the external circuit and if the number of turns in winding I2 is equivalent to the windings I3 and I4, the two ends of the receiver will be at the same potential and no current will flow thru the receiver R, thereby providing the well-known anti-side tone circuit.

This type of anti-side tone circuit is analogous to the well-known Edison three wire circuit in which the windings I3 and I4 act as one generator and the winding I2 acts as a second generator and in which the receiver is included in the neutral wire and is connected at one end to the junction point of the artificial line and line load and at the other end to the junction point of the two generators connected in series. As is wellknown, if the line load and artificial line load are equal no current will flow over the neutral wire thru the receiver.

Considering now the action of the substation during receipt of talking current and also assuming that the volume control switch 3 is operated to engage spring 5 thereby including the entire receiver coil winding in .circuit. It should be mentioned at this time that the impedance of the full winding of the receiver including both portions I and 8 matches the impedance lookin toward the line from points 30 and 3|. As is well-known this matching of impedances gives the maximum transference of energy from the circuit to the receiver.

During the time that the substation is receiving incoming signals an E. M. F. will be present.

across the line conductors I and 2, this E. M. F. being alternating and proportional to the strength of the signal that is being received. The current flowing in over conductor 2 and condenser l5 tends to divide into two paths, the one thru the artificial line comprising condenser 9 and the winding I2 of the auto-transformer and the other path including the full winding of the receiver R, springs 5 and 3, the windings I4 and I3 of the auto-transformer, line conductor I and thence back to the external circuit. The current flowing thru the windings I3 and I4 induces in the winding I2 an electro-magnetic force in such a direction as to oppose the flow of current thru the artificial line. The transmitter circuit at springs 6 may be opened or closed with very little effect in either position but with the springs closed the transmitter is connected in parallel with the winding I4 thereby providing a parallel path for some of the alternating current during receiving. This arrangement introduces a certain loss which is unavoidable and not particularly serious. From the foregoing it will be seen that a majority of the incoming siagnals traverse the receiver coil winding and are effected very little by the shunt path thru the condenser 9 and winding I2.

As previously stated the type of receiver used in this circuit is of the sound powered type such as shown in Patent 2,241,105 and when the impedance in the entire coil winding of the receiver -matches the impedance looking toward the line from the points 30 and 3| the maximum transference of energy to the receiver is attained. On long lines the output level of this receiver when used in this circuit was found to be very satisfactory but when the entire winding of the receiver was used on short line the output level of this receiver was too high and annoying. In order to reduce the output level of the receiver a tap connection is made to only a portion of the receiver coil winding to include the proper impedance to introduce a 12 decibel loss. As shown in the drawing a volume control receiver switch 3 is provided in the handle of the handset to enable the user to use only the portion I of the receiver coil winding or the entire winding including both portions I and 8. Since the circuit is designed so that the impedance of the entire receiver winding including both portons I and 8 matches the impedance when looking toward the line from points 30 and 3|, maximum transference of energy to the receiver is attained with the volume control receiver switch 3 in contact with spring 5. When this circuit is connected to a short line the output level of the receiver is too high for ordinary use and the user will operate the switch 3 to engage spring 4 thereby including only the portion I of the receiver winding in the circuit. The impedance of the receiver, now including only the portion I, no longer matches with the result that approximately a 12 decibel loss is attained thereby bringing the output level of the receiver to approximately the same level as in an ordinary telephone receiver. The loss is due to mismatching of impedance and by reducing the number of turns of the receiver winding included in the receiver circuit.

I am aware that it is old to vary the strength of the signal delivered to a receiver by means of external resistances or external impedances to increase or decrease the output level of said receiver, but so far as I am aware, this is the first time that the output level of a receiver may be varied while receiving the same strength of signal. In accordance with the present invention this latter variation of receiver output level is varied by varying the impedance of the receiver by including only a portion of the receiver winding in the receiver circuitor by changing the impedance of the receiver by including the entire winding of thereceiver winding in the receiver circuit.

What is claimed is:

1. In a substation circuit, a line, a transformer having three windings, a receiving circuit including a volume control receiver switch and receiver connected in series with a first and a second winding of said transformer and the conductors of said line, a third winding of said transformer and a condenser in serial relation connected in shunt of said receiver for forming an anti-side tone circuit; a transmitter and a local battery in series connected in shunt of said second winding of said transformer, a winding in said receiver and means including said connection extending from the second volume control receiver switch for including all the turns of said receiver winding or only a portion of the turns of said receiver winding in said receiving circuit.

2. In a substation circuit, a line, a transformer having three windings, a receiving circuit including a receiver and a volume control receiver switchconnected in series with a first and a second winding of said transformer and the conductors of said line, a third winding of said transformer and a condenser in serial relation connected in shunt of said receiver for forming an anti-side tone circuit, a transmitter connected in shunt oi said second winding of said transformer, a winding in said receiver, and means including said volume control receiver switch for at will including all the turns of said receiver winding or only a portion of the turns of said receiver-winding in said receiving circult.

3. in a substation circuit, a line, a transformer having three windings, a handset including a transmitter and a receiver, a volume control receiver switch and a transmitter key mounted on the handle of said handset between the receiver and transmitter, a receiving circuit including said switch and receiver connected in series with a first and a second winding of said transformer to said connections to operated position of said switch with respect to said connections to said third and second terminals, a first and a. second winding of said trans-- former and the conductors of said line connected in series with said receiver circuit for translating the incoming voice signals, a transmitter circuit including said transmitter connected in shunt of said second winding of said transmitter, and a third winding of said transformer and a condenser in serial relation connected in shunt of said receiver circuit for forming an the entire winding of said receiver or only a portion of said receiver winding dependent upon the operated position of said switch with respect said one terminal and said tap connection, a nrst'and a second windand the conductors of said line, a third winding of said transformer and a condenser in serial relation connected in shunt of said receiver to form an anti-side tone circuit,'a transmitter cir-' cuit including said key and transmitter in se rial relation connected in shunt of said second winding of said transformer. said keyproviding means for at will opening and closingsaid transmitter circuit, a winding in said receiver, and means including said switch for at will including all the turns of said receiver winding or only a portion of the turns of said receiver winding in said receiving circuit.

41-. In a substation circuit. a line, a trormer having three windings, a handset including a transmitter and a receiver, a volume control receiver switch mounted on thejhandie of said handset between saidtransmitter and receiver, a receiving circuit including said switch and receiver connected in series with a first and a second winding ofsaid transformer endthe conductors. of saidline, a third 'winding of said transformer and a condenser inserial relation connected in shunt of said receiver to form ananti-side tone circuit, a transmitterlcircuit in cludingsald transmitter connected in shunt of said second winding of said transformer, a.winding in said'receiver, and means including said switch for at will including all-the turns of said receiver winding or only a portion of, the turns of said receiver winding in said receiving cir- 5. In a substation circuit, a line, a transformer having three windings, a transmitter, a receiver having three terminals, 2.. receiver winding hav ing a plurality of turns connectedbetween the first and third of said receiver terminals, a tap of said receiver terminals to one of the intermediate ing of said transformer and theconductors of said line connected in series with said receiver circuit for translating incoming voice signals, a transmitter circuit including said transmitter connected inshunt or said second winding of said transformer, and a third winding of said transformer and a condenser in serialjrelation connectedin shunt ofsaid receiver circuit for forming an anti-sid tone circuit.- 1 a 7. In a substation circuit, a line, a transformer I having three windings and a condenser connected inseries in bridge of the line conductors of saidline, a transmitter'connected in bridge or I one oi said windings, a receiver connected in bridge of said condenser and another, of said windings, said receiver having a winding whose impedance matches the normal said substation circuit at the points where said receiver is connected into said substation cirmediate point in said receiver cult, a tap connection extending'from an interwindin t a first receiver circuit including the entire receiver winding thereby matching the receiver with respect to. said f'to secure the greatest output level fromsaid returns ofs'aid'receiverwlnding, a volume control receiver switch having connections to said 'sec-. 0nd and; third terminals for said" receiver and means for switchingbetween s'uch connections extending'to said second and third terminals, a receiver circuit including said switch and either thefentire receiver winding. 'audsaid first .ter-

vrninal or. only a pcrtion'ci' said receiver wind; 75

impedanc mediate point in ceiver in response to incoming signalala second receiver circuit including said tap connection,

and only a portiorrof said ,receiver winding thereby mic-matching thejimpedance of.. the receiver with respect to the impedance of said subf station circuit to introduce a .loss in the output level from said receiver in response to incoming signalsof the same-strength as were received in said, first receivercircuit, and a switching I key for switching the substation circuit at will from one of said receiver circuits to the other ofsaid-re'ceiver circuits dependent upon the out put leveldesired from said receiver.

In a substation circult includingline conductors, a transiormena transmitter andya rereceiverhaving a; winding whose. matches :the normal impedance oi said substation circuit at the points where I receiver-is connectedjdntothe substation cir-;-

a tap connection' extendingirom an inter i said receiver winding, aflrst ceiver, 's d receiver circuit. including the 1 entire receiver winding thereby matching the impedance of impedance, of

impedance of-the substation circuit the receiver with respect to said substation circuit to secure the greatest output level from said receiver in response to incoming signals, a second receiver circuit including said tap connection and only a portion of said receiver winding thereby mis-matching the impedance of the receiver with respect to the impedance of said substation circuit to introduce a loss in the output level from said receiver in response to incoming signals 01' the same strength as were received in said first receiver circuit, and a switching key for switching the substation circuit at will from one oi said receiver circuits to the other of said receiver circuits dependent upon the output level desired from said receiver.

ALBERT E. WOODRUFF. 

